Beam generating system for electron tubes with a high breakdown strength



Dec. 12, 1967 MEYERER ET AL 3,358,173

BEAM GENERATING SYSTEM FOR ELECTRON TUBES WITH A HIGH BREAKDOWN STRENGTH Filed April 12, 1965 Hllll United States Patent BEAM GENERATING SYSTEM FOR ELECTRON TUBES WITH A HIGH BREAKDOWN STRENGTH Paul Meyerer, Ottobrunn, and Artur Kraus and Arno Hinckeldey, Munich, Germany, assignors to Siemens Aktiengesellschaft, a corporation of Germany v Filed Apr. 12, 1965, Ser. No. 447,574 Claims priority, applicgtigaiggirmany, Apr. 15, 1964,

11 Claims. (a. 31382) ABSTRACT on THE DISCLOSURE The invention relates to a beam generating system for the generation of a magnetically focused electron beam of great current density for high-power tubes, especially traveling wave tubes, in which the cathode and the focussing electrode (Wehnelt electrode) are centered with respect to and completely accommodated in a cup-shaped shieldingcylinder. In high-power tubes extremely high demands are made on the electron guns in respect to breakdown (dielectric) strength. The individual electrodes of such an electron gun must, therefore, be formed, arranged and mounted insuch a manner that no excessively high electric field strengths occur, through which, then, for example, flashover might take place as a result of field emission.

The difficnlties enumerated occur, as a practical matter, only in traveling wave tubes with only one anode, and less or not at all in so-called three-electrode systems. On the other hand, in the case of tubes with two anodes independent of one another and with considerably diiferent potentials, there may occur between the individual electrodes, disposed within a shielding cylinder, considerable field emissions which may develop in consequence of peak effects in insulating bodies exposed to high electric field strengths.

There has previously become known a beam generating system for a high-power tube, in which, as a shielding member in the region of the insulating wall portion, there is provided a long metal cylindrical member, lying on cathode potential, which cylinder extends about to the lead-through member or plate, and on the other end of which the cathode and the focussing electrode are mounted. For the avoidance of possible voltage breakdowns, the insulating glass wall portion, immersed in oil, is constructed with double walls in such a manner that the interspace so formed is connected bver a narrow annular gap with the interior of the vessel, that is, with the vacuum chamber. This known electrode arrangement, utilized in a so-called three-electrode beam generating system, that is, in a system with only one anode, is not usable for a four-electrode system, that is, for a system with two anodes of high differing potential independent of one another. The known arrangement, therefore, is practically useless for specific electrode systems in which interference manifestations occur in consequence of field emissions in the case of disposition of the electrodes in a common shielding cylinder. A further inherent drawback of the known arrangement, of particular importance, re-

3,35 8,l73 Patented Dec. 12, 1967 P Ce sides in the fact that the focussing electrode lies on cathode potential, and therefore on a fixed potential, and, accordingly, cannot be utilized for control of the electron beam by variation of its potential.

The problem basic to the invention is that of providing in a four-electrode beam generating system, that is a system with two separate anodes, for the generation of an electron beam of high current density, a high breakdown strength and, moreover, to take care that the described drawbacks, as far as possible, are avoided.

This is achieved, according to the invention, in a beam generating system for the generation of a magnetically focussed electron beam of high current density, especially for high-power tubes (as described in the first paragraph), in which the electrode system, consisting of cathode and focussing electrode, centrally is accommodated in a cup-shaped shielding cylinder, by an arrangement in which the shielding cylinder is as a part of the first anode (accelerating anode) and serves as a supporting tube for the electrode system (cathode-focussing electrode).

Further details as well as further features of the invention are explained with the aid of the example of construction of a traveling wave tube, purely schematically represented in the drawing, in which those parts which do not absolutely contribute to the understanding of the invention have been omitted or remain undesignated.

In the drawing, the reference numeral 1 designates the first anode, that is, the accelerating anode, which is formed as a cylindrical member, closed on one end except for a beam aperture, and serves as shielding for the system, for which reason it is designed relatively long so that it extends about as far as the lead-through member or plate 2 or its metal cap 3. The accelerating anode is attached, above the lead-through plate 2, to a formed metal ring 4 which serves as a closure for the discharge vessel, the tube flange 5 being disposed concentrically to the outer ceramic tube 7, which forms part of the vessel wall, and connected therewith by a plate 6 which is joined vacuum-tight with both the ring 4 and the ceramic tube 7. At the other end, the ceramic tube 7 is connected vacuum-tight to the cup-shaped member 8 by a metal connecting ring, the ceramic tube thus functioning as an insulator between the first and second anodes. In the cupshaped metal cylinder 8, opposite the accelerating anode 1, there is attached, vacuum-tight, the second anode 9, and concentrically thereto, the further vessel wall portion 10 of the narrow elongated tube part of the traveling wave tube. Advantageously accelerating anode 1 is formed as a central supporting tube, in the interior of which is disposed the electrode system, consisting of the cathode 11 and the focussing electrode 12. For this purpose, encircling the electrode system is a cylindrical guide tube or cylinder 13, open at both ends and so connected with the electrode system that the self-supporting system, mounted on only supporting wires or rods 14 over the lead-through member 2 likewise carries the guide tube 13. The electrode system 11, 12, with the guide tube 13, is centrally inserted into the accelerating anode, positioned by a stop on the accelerating anode, soldered or welded between the metal cap 3 of the lead-through plate and the metal closed ring 4 at the cooperable cylindrical parts thereof. Such insertion of the electrode system in the carrier tube of the accelerating anode say, in a stacked manner, has, among others, the important advantage that, if necessary, one of the electrodes of the electrode system, especially the cathode, can easily be replaced without damaging the rest of the discharge vessel. The electrode system 12, 13 is constructed with spacing and supporting bars 15, constructed for example of aluminum oxide, and connected with the guide tube 13, utiliz- 3 3 ing soldered or cemented connections. In operation the second anode lies on ground potential, while for example 14 kv. is applied to the first anode and about 16' kv. to the cathode. In the interior of the accelerating anode, which serves as a shielding cylinder, however, practically no appreciable electric fields are present which might give rise to disturbances in consequence of field emission.

The beam generating system according to the invention is usable not only for traveling wave tubes but also for frequency modulation tubes of all kinds.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A beam generating system for the generation of a magnetically focussed electron beam of great current density in high-power tubes, especially traveling wave tubes, said system comprising a cup-shaped member, a cathode, a focussing electrode and a first anode disposed in said cup-shaped member, said first anode constructed in the form of a shielding cylinder and serving as a supporting tube for the cathode and the focussing electrodes.

2. A beam generating system according to claim 1, including a lead-in member, a second anode with considerably differing potential than the potential of said first anode, in which the first anode comprises a relatively long cylindrical member serving as the supporting tube, and extending to said lead-in member.

3. A beam generating system according to claim 1, further comprising a ceramic tube coaxially surrounding one end of said first anode and supporting said cupshaped member at one end thereof, a formed metal ring secured to the other end of said ceramic tube, a metal cap secured between said ring and said lead-in member, and wherein said first anode is attached at the interior of said formed metal ring.

4. A beam generating system according to claim 1, comprising in further combination, a guide cylinder, open at both ends, disposed concentrically about the cathode and focussing electrodes a lead-in member, a plurality of supporting wires extending from said lead-in member to said cathode and focussing electrodes, said cylinder being supported with said cathode and focussing electrodes on said supporting wires, which cylinder is disposed within said supporting tube for the system, which forms said first anode, said supporting tube being provided with an internal stop against which said guide cylinder may bear.

5. A beam generating system as defined in claim 4, further comprising a plurality of supporting elements secured between said guide cylinder and said cathode and said focussing electrodes and a plurality of spacing elements secured between said supporting elements,

6. A beam generating system according to claim 5, wherein said supporting and spacing elements are constructed of aluminum oxide.

7. A four-electrode electr'on tube of the magnetically focussed electron beam type, comprising a cathode, a focussing electrode spaced from said cathode, a cylindrically shaped accelerating anode supporting said cathode and said focussing electrode coaXially therein, a lead-in member, a ceramic tube surrounding said accelerating anode, a second anode supported at one end of said ceramic tube, and a metallic member secured to the other end of said ceramic tube, to one end of said accelerating anode, and to said lead-in member.

8. An electron tube as defined in claim 7, further comprising a guide cylinder disposed concentrically about said cathode and said focussing. electrode and concentrically within said accelerating anode, electrical insulating means for supporting said cathode and said focussing electrode within said guide cylinder, and a plurality of supporting wires connected between said lead-in member and said cathode and focussing electrode.

9. An electron tube as defined in claim 8, wherein said electrical insulating means includes supporting elements secured between said guide cylinder and said cathode and focussing electrodes and spacing elements secured between said supporting elements.

10. An electron tube as defined in claim 9, wherein said supporting and spacing elements are constructed of aluminum oxide.

11. An electron tube of the magnetically focussed electron beam type, comprising a cathode, a focussing electrode coaxially spaced from said cathode, an accelerating anode in the form of an elongated cylinder, electrical insulating means for supporting said cathode and said focussing electrode coaxially within said accelerating anode at one end thereof, a generally cylindrical housing surrounding said accelerating anode and including a ceramic tube disposed coaxially with at least the other end of said accelerating anode, a second anode mounted at one end of said ceramic tube coaxially spaced from the one end of said accelerating anode, and electrically conductive means connected between the other end of said accelerating anode and the other end of said ceramic tube.

References Cited UNITED STATES PATENTS 9/1951 Cage 313- 10/1960 Heil et a1. 313-82 

1. A BEAM GENERATING SYSTEM FOR THE GENERATION OF A MAGNETICALLY FOCUSSED ELECTRON BEAM OF GREAT CURRENT DENSITY IN HIGH-POWER TUBES, ESPECIALLY TRAVELING WAVE TUBES, SAID SYSTEM COMPRISING A CUP-SHAPED MEMBER, A CATHODE, A FOCUSSING ELECTRODE AND A FIRST ANODE DISPOSED IN SAID CUP-SHAPED MEMBER, SAID FIRST ANODE CONSTRUCTED IN THE FORM OF A SHIELDING CYLINDER AND SERVING AS A SUPPORTING TUBE FOR THE CATHODE AND THE FOCUSSING ELECTRODES. 